The use of blood phase partitioning, thixotropic, gel-like materials in blood collection devices to automatically provide a partition barrier between the centrifugally separated blood phases is well known. For example, mixtures of silicone and silica powders are disclosed in U.S. Pat. Nos. 3,852,194 and 4,049,692, the disclosures of which are incorporated herein by reference. Other mixtures such as a mixture including liquid polybutene, polybutadiene or polymer, and one or more silica powders are also now well known blood phase partitioning materials. These gel-like mixtures are formed so that they have a specific gravity between those of the separated low and high density phases so that the material forms a barrier between the separated phases.
Such gel-like materials or sealants have been placed in the bottom of the collection container or tube, as in the above-mentioned U.S. Pat. No. 3,852,194. Some of the problems resulting from such an arrangement have been that the descending high density cellular phase and the ascending gel-like material collide under centrifugal forces which can cause red cell hemolysis and the gel-like material to carry red cells to the blood phase interface zone in the tube. In either case, there may be contamination of the low density phase, serum or plasma, which may result in inaccurate test results. Also, such collision between the gel-like material and the cellular phase components tends to delay the complete formation of the phase partitioning barrier thus requiring longer centrifugation at greater cost. On the other hand, in some cases, the barrier may be formed too soon, causing cells to be trapped in the light phase and contamination.
In U.S. Pat. No. 3,963,119, a silicone-silica material in a dispenser is placed in the open end of a container tube of blood and the device is centrifuged to separate the blood phases and form a phase partitioning barrier. In that construction, the gel-like material flows downwardly toward the interface zone instead of up through the cellular phase. However, such a system requires that the blood filled tube be opened to insert the gel-like material. This presents the danger that blood components of the sample will contact the person handling the container and subject that person to possible disease. Also, airborne matter can enter the sample and affect test results.
In U.S. Pat. No. 3,986,962, a sealant dispenser is inserted into a socket of a stopper such that during centrifugation, the sealant will flow downwardly out of the dispenser to the phase interface to form a barrier. The dispenser has a tubular body with a relatively narrow central conduit which receives the needle during the blood filling of the tube. The gel-like material or sealant is disposed between the outside surface of the conduit and the inner sidewalls of the tubular body. With such a construction there is considerable chance that the blood filling needle will enter the sealant instead of the conduit. If the conduit is made larger, the space for the sealant would be decreased. Also, the dispenser allows substantially unrestricted sealant flow which, in some cases, may produce a barrier across the tube before all the cells have been centrifuged to the bottom portion of the tube.